Method for manufacturing a film on a flexible sheet

ABSTRACT

A method for manufacturing a film, notably monocrystalline, on a flexible sheet, comprises the following steps: providing a donor substrate, forming an embrittlement zone in the donor substrate so as to delimit the film, forming the flexible sheet by deposition over the surface of the film, and detaching the donor substrate along the embrittlement zone so as to transfer the film onto the flexible sheet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry under 35 U.S.C. § 371 ofInternational Patent Application PCT/EP2018/079796, filed Oct. 31, 2018,designating the United States of America and published as InternationalPatent Publication WO 2019/086503 A1 on May 9, 2019, which claims thebenefit under Article 8 of the Patent Cooperation Treaty to FrenchPatent Application Serial No. 1760272, filed Oct. 31, 2017.

TECHNICAL FIELD

The present disclosure relates to a method for manufacturing a film,notably monocrystalline, on a flexible sheet.

BACKGROUND

The formation of a film, notably monocrystalline, on a flexible sheet isnot easy to accomplish.

Indeed, the flexible sheets of interest do not in general have a seedsurface suited to the growth of a film of good crystalline quality.

Furthermore, techniques of bonding a film on a flexible sheet are alsodifficult to implement, because the surfaces to be placed in contact maynot be sufficiently smooth to enable direct bonding. On the other hand,the flexibility of the sheet makes good application against the filmdifficult.

Furthermore, numerous adhesives would be unsuitable in view of their toohigh rigidity in view of the application. These adhesives may also proveto be unsuitable in view of their incompatibility with the heattreatments that can be necessary for shaping the monocrystalline film.

BRIEF SUMMARY

One aim of the present disclosure is thus to conceive a method formanufacturing a thin film, notably monocrystalline, on a flexible sheet,while ensuring good mechanical strength of the transferred layervis-à-vis the receiving sheet.

To this end, the present disclosure describes a method for manufacturinga film, notably monocrystalline, on a flexible sheet, which comprisesthe following steps:

-   -   providing a donor substrate,    -   forming an embrittlement zone in the donor substrate so as to        delimit the film,    -   forming the flexible sheet by deposition on the surface of the        film, and    -   detaching the donor substrate along the embrittlement zone, so        as to transfer the film onto the flexible sheet.

“Flexible” is taken to mean in the present text a sufficiently lowrigidity to allow an elastic deformation during the application ofexternal mechanical stresses. Typically, for the targeted applications,the rigidity is less than or equal to 10⁶ GPa.μm³.

Depending on the targeted applications, a certain flexibility may besought because the targeted object is capable or has to be able todeform without deteriorating, such as, for example, a chip card orinstead a patch that has to follow the movements of the part of thehuman body on which it is applied. A certain flexibility may also besought because the object is intended to be applied in a permanentmanner on a surface with fixed but curved geometry, such as, forexample, bottles, cylindrical recipients, windscreens, etc.

According to one embodiment, the formation of the embrittlement zone iscarried out by implantation of ionic species in the donor substrate.

The implanted ionic species are advantageously hydrogen and/or helium.

According to one embodiment, the detachment of the donor substrate iscaused by a heat treatment.

In a particularly advantageous manner, the film is made of a materialselected from semiconductor materials, piezoelectric materials, magneticmaterials and functional oxides.

The thickness of the film is generally between 100 nm and 10 μm,preferably between 100 nm and 1 μm.

Advantageously, the flexible sheet is made of a material selected frommetals, glasses and ceramics.

The thickness of the flexible sheet is generally between 1 and 50 μm.

The deposition of the flexible sheet may be implemented by one of thefollowing techniques: physical vapor deposition, chemical vapordeposition, electrochemical deposition, spin coating, lacquering andspraying.

Preferably, the flexible sheet has a rigidity R between 100 GPa.μm³ and10⁶ GPa.μm³, the rigidity being defined by the formula:

$R = \frac{E \times H^{3}}{12 \times \left( {1 - v^{2}} \right)}$

where E is the Young's modulus of the material of the sheet, H thethickness of the sheet and v the Poisson coefficient.

The method may comprise, before the formation of the flexible sheet, theformation of an intermediate layer by deposition on the surface of thefilm.

According to one embodiment, the intermediate layer may be configured toincrease the adherence of the flexible sheet vis-à-vis the film.

Optionally, the intermediate layer may form an electrical contact withthe film.

Furthermore, the method may comprise, after the detachment of the donorsubstrate, the deposition of an additional film on the face of thetransferred film opposite to the support.

Advantageously, the residue of the donor substrate at the end of thedetachment is recycled with a view to the implementation of a new film.

In the case where the donor substrate has a non-flat surface obtainedbefore the formation of the embrittlement zone, before the recycling,the residue of the donor substrate is subjected to an operation ofregeneration of its surface involving a removal of material that issubstantially zero or conforming to the topology of the residue.

According to one embodiment, the donor substrate comprises a pluralityof pads laid out on the surface of a wafer, each pad comprising anembrittlement zone delimiting a respective film to transfer, and theflexible sheet is deposited on the surface of the pads.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present disclosure willbecome clear from the detailed description that follows, with referenceto the appended drawings, in which:

FIG. 1A is a schematic cross-sectional view of a donor substrate;

FIG. 1B illustrates in a schematic manner the formation of anembrittlement zone in the donor substrate of FIG. 1A;

FIG. 1C illustrates in a schematic manner the deposition of the flexiblereceiving sheet on the donor substrate of FIG. 1B;

FIG. 1D illustrates in a schematic manner the structure resulting fromthe detachment of the donor substrate along the embrittlement zone;

FIG. 1E illustrates the deposition of an additional film on thetransferred film at the end of the detachment;

FIG. 2A illustrates in a schematic manner the formation of anembrittlement zone in the donor substrate;

FIG. 2B illustrates in a schematic manner the deposition of anintermediate layer on the donor substrate of FIG. 2A;

FIG. 2C illustrates in a schematic manner the deposition of the flexiblereceiving sheet on the intermediate layer of FIG. 2B;

FIG. 2D illustrates in a schematic manner the structure resulting fromthe detachment of the donor substrate along the embrittlement zone;

FIG. 3A illustrates in a schematic manner a donor substrate having acurved surface;

FIG. 3B illustrates the formation of an oxide layer on the surface ofthe donor substrate of FIG. 3A;

FIG. 3C illustrates the formation of an embrittlement zone in thesubstrate of FIG. 3B;

FIG. 3D illustrates in a schematic manner the deposition of the flexiblesheet on the donor substrate of FIG. 3C;

FIG. 3E illustrates in a schematic manner the structure resulting fromthe detachment of the donor substrate along the embrittlement zone;

FIGS. 4A-4D illustrate in a schematic manner the steps of a methodaccording to another embodiment of the present disclosure, involving theformation of a non-flat topology of the surface of the film to transfer;and

FIGs. 5A-5C illustrate in a schematic manner the steps of a methodaccording to another embodiment of the present disclosure.

For reasons of legibility of the figures, the different elements are notnecessarily represented to scale. Reference signs present from onefigure to the next represent the same elements.

DETAILED DESCRIPTION

Generally speaking, the present disclosure provides for the formation ofthe flexible sheet by deposition on a donor substrate that has beenembrittled beforehand so as to delimit a thin film. The thin film isnext transferred onto the flexible sheet by detachment of the donorsubstrate. The sheet may be constituted of a single material or a stackof at least two different materials, deposited successively on the donorsubstrate.

FIG. 1A illustrates a donor substrate 10, which comprises at least onesuperficial portion constituted of the material intended to form thethin film. Although the donor substrate is represented in the form of abulk substrate, it could also be formed of a stack of layers ofdifferent materials, of which a superficial layer constituted of thematerial intended to form the thin film. In particular, the thin filmmay correspond to a layer of this stack produced by epitaxy.

Advantageously, the material intended to form the thin film is selectedfrom: semiconductor materials (e.g., silicon, silicon carbide,germanium, III-V compounds such as AsGa, InP, GaN, II-VI compounds suchas CdTe, ZnO), piezoelectric materials (e.g., LiNbO₃, LiTaO₃, PZT,PMN-PT), magnetic materials and functional oxides (e.g., ZrO₂, YSZ:yttrium stabilized ZrO₂SrTiO₃, GaO₂). These examples are not limiting.

Preferably, the material intended to form the thin film ismonocrystalline. It may also be polycrystalline, and in this caseemphasis is often placed on optimizing its conditions of formation inorder to obtain, for example, a particular density and a size ofcrystalline grains and/or a preferential crystalline orientation, and/oran optimized roughness.

With reference to FIG. 1B, an embrittlement zone 11, which delimits asuperficial film 12 intended to be transferred, is formed in the donorsubstrate 10.

The thickness of the transferred film is defined by the depth of theembrittlement zone 11 in the donor substrate 10. Advantageously, thisdepth is between 100 nm and 10 μm, preferentially between 100 nm and 1μm.

The formation of the embrittlement zone 12 in the donor substrate 10 maybe carried out by implantation of ionic species (shown schematically bythe arrows in FIG. 1B). Advantageously, the implanted species arehydrogen ions and/or helium ions. The implantation energy makes itpossible to define the depth of the embrittlement zone 11. Theimplantation dose is chosen in order to enable the detachment of thefilm 12 after the application of a suitable treatment. The implantationdose is chosen sufficiently low so as not to induce the formation ofbubbles as of the implantation step. The ionic species, the energy andthe implantation dose are chosen as a function of the material of thedonor substrate 10. These conditions have been the subject of numerouspublications and are known in the art.

With reference to FIG. 1C, a flexible sheet 20 is formed on the surfaceof the film 12, which, at this stage, still forms part of the donorsubstrate 10.

In contrast to bonding techniques, the flexible sheet is not a separate,previously formed structure, but instead is formed directly on the donorsubstrate. The following deposition techniques may be implemented forthe formation of the film: physical vapor deposition (PVD), chemicalvapor deposition (CVD), deposition by electrodeposition orelectroforming (electroplating or electrochemical deposition (ECD)),spin coating, lacquering and spraying. These techniques are known per seand will not be described in greater detail here, those skilled in theart being capable of selecting the most suitable technique as a functionof the material of the flexible sheet. Deposition techniques atrelatively low temperature are preferred, in order avoid initiatingpremature detachment of the donor substrate.

The flexible sheet is advantageously made of a material selected frommetals (e.g., Ni, Cu, Cr, Ag, Fe, Co, Zn, Al, Mo, W and alloys thereof),glasses and ceramics (e.g., silica (SiO₂), alumina (Al₂O₃),polycrystalline AlN, polycrystalline silicon, polycrystalline SiC).These examples are not limiting.

The thickness of the flexible sheet is typically between 1 and 50 μm.

The rigidity of the sheet has to be sufficiently low to ensure theflexibility of the sheet with regard to the targeted application, butsufficiently high to enable in a first instance the transfer of the film12 onto the sheet 20, and to do so without formation of blisters.

The rigidity R may be estimated by the formula:

$R = \frac{E \times H^{3}}{12 \times \left( {1 - v^{2}} \right)}$

where E is the Young's modulus of the material of the sheet, H thethickness of the sheet and v the Poisson coefficient.

Sufficiently low rigidity to ensure flexibility is taken to mean arigidity less than or equal to 10⁶ GPa.μm³. As an indication, it will benoted that the rigidity of a layer of 43 μm of silicon is around 10⁶GPa.μm³, whereas the rigidity of a layer of 92 μm of silicon is around10⁷ GPa.μm³.

Sufficiently high rigidity to avoid the formation of blisters during thetransfer is taken to mean a rigidity greater than or equal to 100GPa.μm³.

Furthermore, care is taken to ensure that the adherence of the sheet onthe donor substrate is sufficient to avoid the detachment of the sheetduring the film transfer method. This adherence may be improved by thedeposition of an adhesion layer on the donor substrate before thedeposition of the sheet. For example, such an adhesion layer may be madeof one of the following materials: Ti, Cr, Pt, Ta, TiW, Si₃N₄, TiN,CrCu.

More generally, at least one intermediate layer may be deposited on thefilm 12 before the deposition of the flexible sheet. It may also be, inparticular, a stack of layers. Apart from a potential adhesion function,such an intermediate layer or stack may notably have the function ofavoiding the diffusion of chemical species to the film 12 during thedeposition of the sheet 20, and/or to form an electrical contact on thefilm 12, and/or to form an optical index variation, and/or to form areflective layer such as a Bragg mirror and/or instead minimize adiscontinuity in acoustic impedance. Naturally, those skilled in the artare capable of choosing the suitable materials and their thicknessaccording to the mechanical, electrical, optical, thermal, acoustic orchemical function of the intermediate layer or stack.

The thickness of the intermediate layer(s) remains sufficiently low sothat the rigidity of this layer or stack does not adversely affect theflexibility of the sheet.

When an important difference exists between the thermal expansioncoefficients of the sheet and the film (typically a difference greaterthan 5×10⁻⁶ K⁻¹), the material of the sheet is chosen to demonstratesufficient ductility in order that the transferred film does not sufferdamage (for example, of fissure type) during the transfer method.Sufficient ductility is taken to mean that the elastic limit of thesheet is less than the product of the elastic limit of the film and thethickness ratio between the sheet and the film.

With reference to FIG. 1D, the donor substrate 10 is next detached alongthe embrittlement zone 11, so as to transfer the film 12 onto theflexible sheet 20. At the end of this detachment a residue 10′ of thedonor substrate remains, which may potentially be recycled with a viewto another use.

The detachment is caused by a treatment of the stack of the sheet 20 onthe donor substrate 10. The treatment may be, for example, thermal,mechanical or a combination of these two types of treatment. This typeof treatment is well known notably within the context of the SMART CUT™method and thus will not be described in detail here. In the case of aheat treatment, the thermal budget of this treatment is generallygreater than the thermal budget of deposition of the flexible sheet.

The film 12 may potentially serve as a seed for the deposition of anadditional film 13 (cf. FIG. 1E).

The structure formed of the flexible sheet 20 and the film 12 (and apotential additional film) may be used to form devices, which notablyhave applications in microelectronics, photonics or optics. Such astructure may also enter into the manufacture of sensors or transducers,or membranes for fuel cells.

Below are described several examples (non-limiting) of application ofthe method according to the present disclosure.

EXAMPLE 1 Formation of a Lithium Niobate Film on a Copper Sheet

Lithium niobate is a piezoelectric and pyroelectric material remarkablein that it conserves its piezoelectric properties up to hightemperatures. Its Curie temperature is around 1140° C., whereas numerousother materials lose their properties at temperatures on the order of100° C to 250° C. It thus represents an interesting material for systemsexploiting piezoelectricity and/or pyroelectricity in these temperatureranges.

For example, they may be systems for recovering energy by recovery ofthe energy of vibrations and other deformations of a mechanical systemoperating in a hostile environment in temperature ranges above 250° C.They may also be piezo or pyroelectric sensors dedicated to themeasurement of mechanical deformation, temperature or to the exchange ofdata by emission/reception of radiofrequency waves.

To do so, the lithium niobate film has to be able to deform sufficientlyeasily. This material is monocrystalline and of good quality when it isproduced by drawing out of ingots then cut into bulk wafers of severalhundreds of μm thickness. In thin films, when it is produced bydeposition, it is in general polycrystalline, at bestquasi-monocrystalline but with high concentrations of defects. Havingavailable thin films of lithium niobate of good quality on a flexiblesheet makes it possible to address application fields such as portableor wearable sensors (integrated in textiles, for example), and the“Internet of Things” (IoT). These examples are not limiting.

Helium ions are implanted in a lithium niobate substrate 10 so as toform an embrittlement zone 11 and delimit a thin LiNbO₃ film 12 (cf.FIG. 2A). The thickness of the film 12 is on the order of 1 μm.

An adhesion layer 21 constituted of a Cr/Cu alloy is deposited on thefilm 12 by a PVD technique (cf. FIG. 2B). A copper sheet 20 is nextdeposited on the adhesion layer, by an electrochemical depositiontechnique (cf. FIG. 2C). The thickness of the sheet is on the order of20 μm.

Next, an annealing is applied at a temperature of 300° C., in order tocause the detachment of the donor substrate 10 along the embrittlementzone 11 (cf. FIG. 2D).

EXAMPLE 2 Formation of a yttrium stabilized zirconia Film on a Sheet ofNickel

Yttrium stabilized zirconia is generally in the form of polycrystallineceramic, and more rarely in the form of monocrystalline substrate.

One use of this material is based on its ion conduction properties. Itthen serves as solid membrane to play the role of electrolyte in SOFC(Solid Oxide Fuel Cell) systems. Such systems, when they have to beminiaturized (this is then known as micro-SOFC), have interest to evolveon the one hand to thin membranes, typically below several μm thickness,and on the other hand to monocrystalline materials. Such systems operateat high temperature (typically 550° C. -700° C.) and are subjected tostrong thermomechanical loads. In order to make the membrane moreresistant, it will advantageously be given the possibility of deformingslightly.

A monocrystalline YSZ substrate 10 is supplied.

Hydrogen ions are implanted in the substrate 10 so as to form anembrittlement zone 11 and delimit a thin YSZ film 12 (cf. FIG. 2A). Thethickness of the film 12 is on the order of 1 μm.

An adhesion layer 21 constituted of a Cr/Cu alloy is deposited on thefilm 12 by a PVD technique (cf. FIG. 2B). A nickel sheet 20 is nextdeposited on the adhesion layer by an electrochemical depositiontechnique (cf. FIG. 2C). The thickness of the sheet is on the order of20 μm.

Next, an annealing is applied at a temperature of 300° C., in order tocause the detachment of the donor substrate 10 along the embrittlementzone 11 (cf. FIG. 2D).

EXAMPLE 3 Formation of a Monocrystalline Silicon Film on a Curved GlassSheet

In the field of the production of screens or other optical parts(lenses, mirrors, etc.), the production of non-flat or curved partsmakes the use of thin films of monocrystalline materials such as silicondifficult. This example aims to make available a thin silicon film on aglass sheet having a certain curvature. This silicon film could serve toproduce high performance transistors, for example, for the purposes ofproducing high definition ultra-compact and curved screens.

A bulk monocrystalline silicon substrate 10 is supplied.

The curved shape that it is wished to follow is produced by etching inthis silicon substrate. In the case of FIG. 3A, the shape chosen isconcave with a more pronounced rise on the edges. Any otherprofil—parabolic, elliptic, corrugated, etc.—will be possible. Thisshape could be produced thanks to an etching by mechanical machining.Those skilled in the art will know how to adapt the etching technique tothat most suited to the desired shape and dimension.

The substrate 10 is subjected to a thermal oxidation to produce a SiO₂layer 14 of 0.2 μm thickness (cf. FIG. 3B). Hydrogen ions are nextimplanted in the substrate 10 so as to form an embrittlement zone 11 anddelimit a thin film 12 of monocrystalline silicon (cf. FIG. 3C). Thethickness of the film 12 is of the order of 0.5 μm.

A sheet 20 made of silica, in other words made of glass, is deposited onthe film 12 by a deposition technique at low temperature, typicallybelow 200° C. so as not to cause an untimely detachment along theembrittlement zone (cf. FIG. 3D). The thickness of the sheet is of theorder of 20 μm. Those skilled in the art will know how to choose inthese conditions the deposition technique the most suited notably interms of temperature and desired final thickness.

Next, an annealing is applied at a temperature of 500° C., in order tocause the detachment of the donor substrate 10 along the embrittlementzone 11 (cf. FIG. 3E).

EXAMPLE 4

Example 4 targets acoustic wave structures such as radiofrequency (RF)filters, for example. In certain structures it is sought to avoidreflections of parasitic waves on the rear face of the substrates and orlayers considered. One means consists in making geometrically imperfectthe interfaces and rear surfaces, notably by introducing voluntarytexturing or other types of roughness. This constraint is difficult oreven impossible to satisfy if the use of certain thin films ofmonocrystalline materials such as LiTaO₃, for example, are contemplated,and this is so without resorting to the introduction of complex stacksof additional intermediate layers. Example 4 targets such an object.

A bulk monocrystalline LiTaO₃ substrate 10 is supplied.

Hydrogen ions are implanted in the substrate 10 through the surface 10 aso as to form an embrittlement zone 11 and delimit a thin film 12 ofmonocrystalline LiTaO₃ (cf. FIG. 4A). The thickness of the film 12 is onthe order of 1.5 μm.

A texturing of the surface 10 a is created by photolithoetching (cf.FIG. 4B). In this example, the implantation takes place before thetexturing step, but it could take place after.

Those of ordinary skill in the art will know how to adapt the techniqueto that most suited to the shape and dimensions desired for the texture.It is possible, for example, to choose a nanoimprint lithographytechnique to define patterns of characteristic slightly submicroniclateral dimensions, over a depth on the order of 0.05 μm. In analternative, the texturing is obtained by roughening by cathodicsputtering effect. According to another alternative, preferablyimplemented before the implantation step, the texturing may be obtainedby a sanding of the surface of the substrate 10.

A sheet 20 made of silica is deposited on the film 12 by a lowtemperature deposition technique, typically below 100° C. so as not tocause premature detachment along the embrittlement zone (cf. FIG. 4C).The thickness of the sheet is on the order of 10 μm. Those of ordinaryskill in the art will know how to choose in these conditions the mostsuitable deposition technique notably in terms of temperature anddesired final thickness. As an alternative, the sheet 20 may be made ofmetal instead of being made of silica.

Next, an annealing is applied at a temperature on the order of 200° C.,in order to cause the detachment of the donor substrate 10 along theembrittlement zone 11 (cf. FIG. 4D).

EXAMPLE 5 Case of a Donor Substrate Comprising a Plurality of Pads

According to one embodiment of the present disclosure, the non-flattopology of the donor substrate results from the formation of aplurality of pads 1001 laid out on the surface of a wafer 1000 (cf. FIG.5A).

The pads are advantageously formed of a material selected fromsemiconductor materials, piezoelectric materials, magnetic materials andfunctional oxides. The pads are advantageously monocrystalline. Each padmay be put in place on the wafer by bonding, individually orcollectively.

The pads may have any appropriate size and shape as a function of thetargeted application. The pads may be laid out in a regular manner onthe wafer, for example, to form a sort of grid pattern.

The main surface of each pad 1001 is parallel to the main surface of thewafer 1000. However, in so far as the thickness of each pad is notcontrolled with sufficient precision, there may exist a slightdifference in thickness from one pad to the next (for example, on theorder of 1 or 2 μm thickness). As a result, the surface constituted ofall of the surfaces of the pads has differences in levels, typically inthe form of steps (the amplitude of these variations has beenvoluntarily exaggerated in FIG. 5A). These different steps thus form anon-flat topology of the surface of the wafer.

In general, as described, for example, in the documents FR 3 041 364 andU.S. Pat. No. 6,562,127, the pads are intended for the transfer of asuperficial monocrystalline film onto a final support. To this end, anembrittlement zone 1011 is formed in each pad, before or after itsputting in place on the wafer, to delimit a respective film 1012 totransfer, for example, by an implantation as described above.

Unlike the methods described in the aforementioned documents, whichinvolve bonding of the main face of each pad on the final support, thepresent disclosure describes depositing the flexible sheet 20 on all ofthe pads laid out on the surface of the wafer (cf. FIG. 5B). One is thusfree of problems of assembly linked to the difference in height of thedifferent pads.

Next, each pad is detached along the respective embrittlement zone 1011,so as to transfer the corresponding film 1012 onto the flexible sheet 20(cf. FIG. 5C).

Advantageously, the transferred films are more rigid than the flexiblesheet. Consequently, if the use of the composite structure therebyobtained involves deforming it in a permanent or dynamic manner, thesheet constitutes a flexible junction between the pads, which absorbsthe stresses due to these deformations instead of transmitting them tothe pads.

Whatever the embodiment considered, at the end of the detachment of thedonor substrate, a residue 10′ remains.

If a recycling of the donor substrate is desired, it is possible toimplement reconditioning operations, notably with the aim ofregenerating the surface of the donor substrate, which could have beendamaged during the detachment. These operations may notably comprisesteps of cleaning, etching, annealing, smoothing and planarization, forexample, by polishing.

In the case where the donor substrate has a particular topology(curvature, roughness, texturing, etc.) that has been produced beforethe embrittlement step, the residue of the donor substrate has atopology identical to the initial topology of the donor substrate. Itmay appear advantageous for purposes of cost to conserve this topologythat had been initially created in the donor substrate, with a view toavoiding reforming it systematically after each recycling. In this case,planarization methods are avoided, while favoring methods for removingmaterial conformal in thickness, or even with substantially zero removalof material (that is to say below 30 nm), such as, for example, plasmaetchings or smoothing annealings.

The invention claimed is:
 1. A method for manufacturing a film, on aflexible sheet, the method comprising the following steps: providing adonor substrate; forming an embrittlement zone in the donor substrate soas to delimit the film, the film having a thickness between 100 nm and10 μm; forming the flexible sheet by deposition over a surface of thefilm; and detaching the donor substrate along the embrittlement zone soas to transfer the film onto the flexible sheet.
 2. The method of claim1, wherein the formation of the embrittlement zone is carried out byimplantation of ionic species into the donor substrate.
 3. The method ofclaim 2, wherein the implanted ionic species are hydrogen and/or helium.4. The method of claim 1, wherein the detachment of the donor substrateis caused by a heat treatment.
 5. The method of claim 1, wherein thefilm comprises at least one material selected from among: semiconductormaterials, piezoelectric materials, magnetic materials and functionaloxides.
 6. The method of claim 1, wherein the flexible sheet comprisesat least one material selected from among: metals, glasses and ceramics.7. The method of claim 1, wherein the flexible sheet has a thicknessbetween 1 and 50 μm.
 8. The method of claim 1, wherein the deposition ofthe flexible sheet is implemented by at least one technique selectedfrom among: physical vapor deposition, chemical vapor deposition,electrochemical deposition, spin coating, lacquering and spraying. 9.The method of claim 1, wherein the flexible sheet has a rigidity (R)between 100 GPa.μm³ and 10⁶ GPa.μm³, the rigidity being defined by theformula:$R = \frac{E \times H^{3}}{12 \times \left( {1 - v^{2}} \right)}$ whereE is the Young's modulus of a material of the flexible sheet, H is athickness of the flexible sheet, and v is the Poisson coefficient. 10.The method of claim 1, further comprising, before the formation of theflexible sheet, the formation of an intermediate layer by depositionover the surface of the film.
 11. The method of claim 10, wherein theintermediate layer is configured to increase an adherence of theflexible sheet to the film.
 12. The method of claim 10, wherein theintermediate layer forms an electrical contact with the film.
 13. Themethod of claim 1, further comprising, after the detachment of the donorsubstrate, the deposition of an additional film on a face of thetransferred film opposite to the flexible sheet.
 14. The method of claim1, further comprising recycling a remaining portion of the donorsubstrate after the detachment and reusing the donor substrate to form anew film.
 15. The method of claim 14, wherein the donor substrate has anon-flat surface obtained before the formation of the embrittlement zoneand wherein, before the recycling, the donor substrate is subjected toan operation of regeneration of its surface involving a removal ofmaterial from the donor substrate.
 16. The method of claim 1, whereinthe donor substrate comprises a plurality of pads laid out on a surfaceof a wafer, each pad comprising an embrittlement zone delimiting arespective film to be transferred, and the flexible sheet is depositedon a respective surface of each of the pads of the plurality.
 17. Themethod of claim 1, wherein the film is a monocrystalline film.
 18. Amethod for manufacturing a film, on a flexible sheet, the methodcomprising the following steps: providing a donor substrate; forming anembrittlement zone in the donor substrate so as to delimit the film;forming the flexible sheet by deposition over a surface of the film, theflexible sheet having a thickness between 1 and 50 μm; and detaching thedonor substrate along the embrittlement zone so as to transfer the filmonto the flexible sheet.
 19. The method of claim 18, wherein theflexible sheet comprises at least one material selected from among:metals, glasses and ceramics.
 20. The method of claim 18, wherein thedeposition of the flexible sheet is implemented by at least onetechnique selected from among: physical vapor deposition, chemical vapordeposition, electrochemical deposition, spin coating, lacquering andspraying.
 21. The method of claim 18, wherein the flexible sheet has arigidity (R) between 100 GPa.μm³ and 10⁶ GPa.μm³, the rigidity beingdefined by the formula:$R = \frac{E \times H^{3}}{12 \times \left( {1 - v^{2}} \right)}$ whereE is the Young's modulus of a material of the flexible sheet, H is athickness of the flexible sheet, and v is the Poisson coefficient. 22.The method of claim 18, further comprising, before the formation of theflexible sheet, the formation of an intermediate layer by depositionover the surface of the film.
 23. The method of claim 22, wherein theintermediate layer is configured to increase an adherence of theflexible sheet to the film.
 24. The method of claim 22, wherein theintermediate layer forms an electrical contact with the film.